Technical Field
The invention relates to the art of axle/suspension systems for heavy-duty vehicles. More particularly, the invention relates to beams used in axle/suspension systems of heavy-duty vehicles. Even more particularly, the invention is directed to a beam for an axle/suspension system of a heavy-duty vehicle that features a facetted profile and taper from the bottom to the top of the beam, which enables additional jounce travel of the beam during operation of the heavy-duty vehicle, and in the case of a lift axle/suspension system, additional tire clearance from the ground when in the lifted position. With the additional beam jounce travel and clearance enabled by the tapered beam design of the present invention, an axle pass-through box beam design can be utilized with a heavy-duty tractor, trailer, or truck, thereby decreasing the structural complexity and overall vehicle weight, and increasing the fuel economy of the vehicle.
Background Art
The use of air-ride trailing and leading arm rigid beam-type axle/suspension systems has been very popular in the heavy-duty truck and tractor-trailer industry for many years. Although such axle/suspension systems can be found in widely varying structural forms, generally their structure is similar in that each system typically includes a pair of suspension assemblies. In some heavy-duty vehicles, the suspension assemblies are connected directly to the primary frame of the vehicle. In other heavy-duty vehicles, the primary frame of the vehicle supports a subframe, and the suspension assemblies connect directly to the subframe. For those heavy-duty vehicles that support a subframe, the subframe can be non-movable or moveable, the latter being commonly referred to as a slider box, slider subframe, slider undercarriage, or secondary slider frame. For the purposes of convenience and clarity, reference herein will be made to main members, with the understanding that such reference is by way of example, and that the present invention applies to heavy-duty vehicle axle/suspension systems suspended from main members of: primary frames, moveable subframes and non-moveable subframes.
Typically, each suspension assembly of an axle/suspension system includes a pair of longitudinally extending elongated beams. Each beam is located adjacent to and below a respective one of a pair of spaced-apart longitudinally extending main members and one or more cross members which form the frame of the vehicle. More specifically, each beam is pivotally connected at one of its ends to a hanger which in turn is attached to and depends from a respective one of the main members of the vehicle. An axle extends between and is connected by some means to the beams of the pair of suspension assemblies at a selected location from about the mid-point to the end of the beam opposite from its pivotal connection end. The opposite end of each beam also is connected to a bellows air spring or its equivalent, which in turn is connected to a respective one of the main members. A brake assembly and typically one or more shock absorbers also are mounted on each of the beams and/or axle. A height control valve is mounted on the hanger or main member and is operatively connected to the beam or axle in order to maintain the ride height of the vehicle.
The beam may extend rearwardly or frontwardly from the pivotal connection relative to the front of the vehicle, thus defining what are typically referred to as trailing arm or leading arm axle/suspension systems, respectively. However, for purposes of the description contained herein, it is understood that the term “trailing arm” will encompass beams which extend either rearwardly or frontwardly with respect to the front end of the vehicle. The beam on which the axle is mounted is generally referred to as either a bottom-mount/underslung beam, a top-mount/overslung beam, or a pass-through beam which can be generally classified as either an underslung or overslung beam depending on the location of the other components of the axle/suspension system, as is known in the art. Because of the limited distance between the axle/suspension system beams and the vehicle frame main members at ride height in heavy-duty tractor, trailer, or truck applications, an overslung pass-through beam design is generally not utilized for such applications. Therefore, for purposes of the description contained herein, it is understood that the term “pass-through beam” refers to an underslung pass-through beam design.
The axle/suspension systems of the heavy-duty vehicle act to cushion the ride, dampen vibrations, and stabilize the vehicle. More particularly, as the vehicle is traveling over the road, its wheels encounter road conditions that impart various forces, loads, and/or stresses, to the respective axle on which the wheels are mounted, and in turn, to the suspension assemblies that are connected to and support the axle. One of the many forces a heavy-duty vehicle can encounter during normal vehicle operation is the upward force imparted on the axle/suspension system when one of the attached wheels encounters a road hazard, such as a speed bump or curb. In such instances, the upward force is directed to the vehicle wheel, which in turn causes the axle and beam to which it is attached to travel upwardly. The distance the axle/suspension system travels upwardly as a result of the force is known in the art as suspension jounce. An axle/suspension system works to counter the upward force during jounce movement, and return the system to equilibrium, or normal operating ride height. In an axle/suspension system featuring non pass-through overslung beams, the jounce distance the axle/suspension system can travel is limited to the distance between the top of a beam and the bottom of the main member. In an axle/suspension system featuring non pass-through underslung beams, the jounce distance the axle/suspension system can travel is limited to the distance between the top of the axle and the bottom of the main member. In an axle/suspension system featuring pass-through underslung or overslung beams, the jounce distance the axle/suspension system can travel is limited to the distance between the top of a beam and the bottom of the main member.
It also is common practice for an axle/suspension system of a heavy-duty vehicle to feature a lift assembly to enable lifting of one or more of the axles of a heavy-duty vehicle and to maintain the lifted axles in a raised position, which in turn causes the wheels and tires attached to the raised axles to be lifted off of the ground. Removing certain ones of the heavy-duty vehicle wheels and tires from ground contact typically is done when the trailer is free of payload and less than all of the wheels/tires of the vehicle can adequately support the unloaded trailer, or when greater maneuverability of the vehicle is desired. This lifting operation results in reduced wear on the lifted axle, wheels, and tires when the vehicle is traveling in an unloaded condition. Additionally, lifting can result in toll savings as the axles accounted for in determining toll costs are often only those which are in contact with the ground.
An example of a lift axle/suspension system application is in heavy-duty tractors featuring a 6×2 pusher configuration. Heavy-duty tractors generally feature a non-driven steerable axle situated at the front of the tractor, and two additional axles located at the rear of the tractor. Power from an engine disposed at the front of the tractor is transferred to an attached transmission, which through one of many gear ratios, is further transferred by a longitudinally rearwardly-extending driveshaft to one or more rear axles. In a 6×2 pusher configuration, the drive shaft extends to the rearwardmost axle, which is a driven axle. The axle directly in front of the rear axle, typically referred to as the forward tandem axle, is not driven.
In order for the drive shaft to extend to the rearwardmost tandem axle without interference from the forward tandem axle, the forward tandem axle typically features a drop axle design which allows for clearance of the drive shaft. In such designs, the axle features a downwardly-extending or U-shaped curvature at its longitudinal centerline, which allows the driveshaft to extend to the rear driven axle without interference from the forward tandem axle, while maintaining a ride height similar to that of the driven axle. Moreover, when the forward tandem axle is a lift axle, because the axle features a downwardly-extending or U-shaped curvature at its longitudinal centerline, there is clearance for the drive axle to extend to the rear driven axle without interference from the axle even when it is in the lifted position
In heavy-duty tractor applications, prior art lift and non-lift axle/suspension systems typically employ the use of an underslung non pass-through beam design due to the limited clearance beneath the tractor main members that typically prevents use of overslung beam designs. In an underslung beam design, the axle is attached to the top of each beam of the axle/suspension system by a plurality of brackets integrated into the beam and a plurality of U-bolts, which secure the axle to the brackets of each beam. However, axle jounce of the pusher forward tandem axle in an underslung beam configuration is limited by the distance between the frame main member and the axle at ride height. In addition, when the pusher forward tandem axle is a lift axle having an underslung attachment to the beam, clearance between the tires and the ground when the axle is in the lifted position is similarly limited.
In heavy-duty trailer applications, it is common for prior art axle/suspension systems to employ the use of overslung or underslung beam designs since adequate clearance exists beneath the main members of many trailer designs. In a pass-through beam, the axle/suspension system axle is disposed through the rear portion of the beam. Pass-through beams are generally simpler in design, lacking the additional axle seating components such as U-bolts and brackets required to secure an axle to a beam, and thus are generally less complex and lighter compared to non-pass-through overslung and underslung beams. In order to ensure adequate upward travel of the axle/suspension system during vehicle jounce, pass-through beams typically require a higher ride height because the axle jounce travel is limited by the distance between the frame main member and the top of the beam, as compared to the distance between the frame main members and the axle in underslung non pass-through beams. Because of the reduced jounce travel permitted by a much lower ride height in heavy-duty tractors compared to that of heavy-duty trailers, implementing a lift or non-lift axle/suspension system featuring prior art pass-through beams can potentially result in the beams striking the vehicle main members during jounce experienced by the beams as a result of road conditions the vehicle can encounter during operation. This could potentially result in a loss of traction of the rear driven axle, and damage to the beam, vehicle frame, and/or other components of the axle/suspension system. Additionally, because of reduced clearance between the beam and the frame, the vehicle wheels are positioned closer to the ground in a lift axle configuration operating in the lifted position, potentially resulting in damage to the wheels by road debris encountered during operation of the vehicle.
Therefore, a need exists in the art for a heavy-duty axle/suspension system that provides additional beam jounce travel in lift and non-lift axles, and additional ground to wheel clearance in lift axles, so that a pass-through beam can be utilized with a heavy-duty tractor axle/suspension system, resulting in decreased vehicle weight. The axle/suspension system for heavy-duty vehicles of the present invention incorporating the improved beam design satisfies these needs, as will be described below.